1. Field of the Invention
The present invention relates to a television receiver (TV receiver) in which a tuner unit and a monitor unit are separated from each other, the tuner unit transmitting program data to the monitor unit via wireless transmission.
2. Description of the Related Art
In recent years, high-speed wireless LAN systems conforming to the IEEE802.11n standard, one of wireless networks standard, are coming to be used for information transmission between consumer digital information devices. For example, applying such a wireless LAN to a TV receiver in which a tuner unit and a monitor unit are separated from each other, the tuner unit transmitting program data to the monitor unit, eliminates the need of wiring between devices. Further, this configuration attains high-speed large-capacity transmission with a transmission rate of 100M bps or higher, making it easier to transmit large-capacity video data such as Hi-Vision high-definition pictures and the like.
The IEEE802.11n standard prescribes 5 GHz-band communication channels shared with commercial radar systems such as weather radars so as to increase the number of usable channels. However, devices utilizing the shared channels are regulated by the Wireless Telegraph Law so as to give priority to commercial radar systems and so as not to interfere their operations. Such devices are obliged to perform the following operations which are collectively referred to as Dynamic Frequency Selection (hereinafter abbreviated to DFS) operations.
(1) Channel Availability Check (hereinafter abbreviated to CAC): Before network establishment, the device scans radar waves for a minute and then sets an unused channel.
(2) In-Service Monitoring (hereinafter abbreviated to ISM) and Channel Move Time (hereinafter abbreviated to CMT): During regular operation, the device constantly monitors the radar wave of the unused channel. When it detects a radar wave, it stops data transmission through the channel within 10 seconds.
(3) Non-Occupancy Period: For the channel with radar wave detection, the device is not allowed to perform data transmission for 30 minutes since radar wave detection.
The following technique has been proposed in relation to the above-mentioned operations.
JP-A-2007-53726 discloses a technique for preselecting a communication channel with which interference to radar equipment does not occur so that communication channel changeover is not required during real-time video data transmission. Specifically, this technique performs the steps of: determining the possibility of radar wave existence based on information about a position at which wireless communication equipment is installed and on radar information used for identifying radar equipment, including a position at which the radar equipment is installed; and selecting a communication channel of the wireless communication equipment based on the result of the determination.
JP-A-2007-325041 discloses a technique for a wireless LAN channel on which a specific priority radio wave (radar wave) and a frequency band are overlapped. The technique investigates receive conditions of the specific priority radio wave. Specifically, a detection program according to the technique performs the steps of: receiving radio waves by sequentially selecting each wireless LAN channel on which the specific priority radio wave and the frequency band are overlapped, and identifying the specific priority radio wave from the received radio waves based on a predetermined identification criterion; and setting any one channel on which no specific priority radio wave is detected as a channel to be used for the wireless LAN.